This invention relates to an electro-optical method for the inspection of a moving film body by a nondestructive, noncontact method.
Household plastic wraps, like Saran Wrap.RTM. brand plastic film have as primary physical properties, film thickness and surface texture. Film thickness and surface texture determine the quality and the ability of the film to cling to an object. Film thickness can be controlled using on-line process monitoring devices for measuring film thickness and then manipulating the film production in accordance with the detected measurements. Film surface texture, however, is not normally measured continuously on-line and a need has existed to provide a means for continuous on-line monitoring of surface texture to obtain optimum product quality.
The detection of surface texture, particularly where the film is covered with a fluid which varies the thickness and surface conditions of the moving film body is complex. As a result, constantly changing surface conditions require intricate machinery for monitoring surface texture and film imperfections. Thus, a long felt need has existed for a simple, uncomplicated device and a simple and uncomplicated technique which can, in a single measurement, detect apparent gouges and defects on the surface of a film, such as Saran Wrap.RTM. plastic film.
Surface texture of a moving film body can be considered in terms of surface roughness which comprises regularly occurring microscopic and submicroscopic features and irregularly occurring macroscopic features on the film body.
The optical property known as haze can be used to assess the surface texture of a plastic film body. The term "haze" refers to the intensity of light scattered at all angles greater than 2.5 degrees from the direction at which a light beam directly falls on the film. Haze is usually expressed as a percentage, that is, the "haze percent" of the light intensity transmitted directly at the film body. An optical instrument has been needed which is capable of measuring the haze percent for an essentially transparent film body having at least two surfaces which is capable of on-line measurement of the moving film body.